I’m thinking of switching to a bank that uses its mobile app for 2fa. I use a dumbphone flipphone as my daily driver that only has talk and text and is not able to download apps. I do have an old smartphone that is going to stop receiving updates soon. I was wondering if it would be safe to use the mobile banking app for 2fa on the old phone after it stops receiving updates. I would plan on factory resetting the phone and not downloading or using any other app on it (including the browser). It would also have no Sim card in it. I would leave it off and only turn it on and use WiFi for using the banking app for 2fa purposes.